1.Field of the Invention
The present invention relates to wireless resource management methods. More particularly, the present invention relates to a power estimation method in a Multiple Users Reusing One Single time slot (MUROS) system when two users are paired.
2.Description of the Related Art
In theory, MUROS aims to multiplex four GSM-HR mobile stations (for half rate) and two GSM-FR mobile stations (for full rate) onto one time slot, expecting to provide improvement for both the full rate as well as the half rate channels. Thus, MUROS intends to enhance the voice capacity (cell capacity) by pairing two or more users (or mobile stations) onto a single timeslot.
A prerequisite in MUROS is to maintain good link quality for the paired users because the pairing may include a legacy user. Thus, while pairing two users for MUROS, care should be taken that the relative power control and power estimation as calculated by the two users is accurate. More specifically, because paired users in MUROS are in the same time slot (same cell), the paired users face a dominant interference due to each other's presence. Such dominant interference is different from the interference experienced from neighbor cells. Thus, inaccurate power estimation, coupled with the potential for dominant interference, may lead to higher Bit Error Rates (BERs) for the paired users. Moreover, inaccurate power estimation adversely affects channel estimation and further decoding of received information by the user.
For paired users including a legacy user and a MUROS user, the existing system may support the legacy user by boosting the power level for the legacy user while reducing it for the MUROS user. Thus, there is a high risk that the MUROS user may inaccurately estimate its power level by decoding an incorrect signal and thus receive a very high BER from the Base Transceiver Station (BTS) and subsequently report the same high BER to the BTS. This cascading effect will affect the power control leading to further reporting of incorrect BERs by the MUROS user.
Various prior art methods, such as described by US20050099973 and U.S. Pat. No. 6,154,450,discuss methods for power estimation at a BTS by establishing transmission power control based on an estimated inter-cellular interference power level and reception quality to ramp up the transmit power; or a BTS transmitting a power level command to a ‘Mobile Station’ (hereinafter ‘MS’) to ramp up the transmit power value based on a predetermined value obtained by comparing the interference power level from the neighbouring cells. However, these methods do not address the issue when the interference is within the same cell and also involves a MUROS user. Few other known methods for power estimation typically employ least squares techniques that are converging in nature. Such techniques being very slow are inefficient and thus not suitable for a MUROS system. Thus a need is felt to provide a method of power estimation in the users in a MUROS system so as to enable them function efficiently in conjunction with the existing power control mechanisms of a GSM network.